Conventionally, the inspection of defective articles using an X-ray inspection apparatus has been conducted in production lines for foods and other products in order to avoid the shipment of defective articles, such as those that are contaminated with foreign matter or are chipped or broken. This type of X-ray inspection apparatus applies X-rays to articles subject to inspection while the articles are continuously transported, and the transmitted X-rays are detected by an X-ray receiving unit. In this manner, the apparatus identifies whether or not there are contaminants in the inspected articles, the inspected articles are chipped or broken, there is an insufficient number of units inside the inspected articles, and the like. In addition, some X-ray inspection apparatuses perform an inspection in which the number of units inside the inspected articles is counted.
Further, some X-ray inspection apparatuses, for example, create an image by detecting X-rays that were applied to an article subject to inspection, and then determine whether or not the inspected article contains a contaminant based on the data for this image. Because contaminants such as metal, stone, glass, and the like are shown in a color that is darker than target articles such as food, these X-ray inspection apparatuses will extract pixels that are contained in the image and are within a predetermined density range. If the area of a portion of the extracted pixels is larger than a predetermined size, this portion will be determined to be a contaminant.
PCT Publication Number WO98/11456 (republished on Mar. 19, 1998) discloses an X-ray inspection apparatus that is highly selective toward contaminants, and performs a highly sensitive detection of contaminants. This X-ray inspection apparatus provides and combines a plurality of matrix sizes and coefficients for image processing in order to detect contaminants in various samples.